Calculation of the APU Data (hours/cycles)

TASK 49-00-00-860-811-A
Calculation of the APU Data (hours/cycles)

1. Reason for the Job
The reset of the APU hour and cycle counters can cause problems with the monitoring of the APU service life.
The procedures that follow will help the operator know the operational history of the APU, if necessary.
2. Job Set-up Information
A. Referenced Information

REFERENCE	DESIGNATION
TASK 49-00-00-860-011-A	Update of APU Data (hours/cycles)

3. Job Set-up
Subtask 49-00-00-860-202-A ** ON A/C NOT FOR ALL

A. Not Applicable

4. Procedure

NOTE: The three methods that follow give an estimate of the number of APU hours and cycles in relation to a typical duty cycle. To make the estimate of the duty cycle, you can select the method that is the most applicable to your operational requirements.

Subtask 49-00-00-869-052-A ** ON A/C NOT FOR ALL

A. Select the applicable method:
(1) Method 1 - APU operative hours to aircraft Flight Hours (FH) ratio (fleet average).

NOTE: This method uses the average fleet ratios that follow:

APU operative hours to aircraft FH average ratio, and
APU operative hours to APU cycles.

(a) To get representative results, do this calculation during a period of three months.
1 To make an estimate of the APU hours during a period without APU monitoring, multiply the average APU operative hours to aircraft FH ratio by the number of FH during this period.
2 Use the average APU operative hours to cycles ratio to get the APU cycles with the same procedure given in the previous step.

NOTE: The procedure will be applied as many times as the airline specifies.

(2) Method 2 - APU operative hours to aircraft FH ratio (for one aircraft).

NOTE: This method uses the APU operative hours to aircraft FH ratio and the APU operative hours to cycles ratio during a recommended period of three months for one aircraft.

(a) Calculate the ratios of the aircraft.
(b) Use the steps given for Method 1 to know the APU history.
(c) If the available data are for less than three months, do the fleet average method to make an estimate of the APU operating ratios.
(3) Method 3 - APU operative hours to aircraft FH ratio (for one APU serial number (S/N)).

NOTE: This method uses the calculation of the average APU operation in one day for a specific S/N. The data used for this comes from APU operative hours and cycles recorded during the last three months, if available.

(a) Calculate the daily average operation of the APU. Use the APU operative hours and cycles recorded during the last three months.
(b) Multiply the operation rate of one day by the number of days of the period without APU monitoring to get an estimate of the APU hours and cycles for this period.
(c) If there is no data recorded during a minimum of three months available for the specified APU S/N, do the steps given in Method 1 to make an estimate of the APU operating ratios.

Subtask 49-00-00-860-201-A ** ON A/C NOT FOR ALL

B. Update the APU S/N and/or APU cycles and hours data (Ref. AMM TASK 49-00-00-860-011).

5. Close-up
Subtask 49-00-00-860-203-A ** ON A/C NOT FOR ALL

A. Not Applicable

[Rev.10 from 2021] 2026.04.01 01:25:36 UTC